Supermassive Black Hole Merger Spotted with the Aid of a Pulsing Quasar

As two galaxies enter the final stages of merging, scientists have theorized that their supermassive black holes will actually form a "binary," two black holes in such close orbit that they are gravitationally bound to one another. Now, scientists may have uncovered direct evidence of black hole binaries.

"We believe we have observed two supermassive black holes in closer proximity than ever before," said Suvi Gezari, co-author of the new study, in a news release. "This pair of black holes may be so close together that they are emitting gravitational waves, which were predicted by Einstein's theory of general relativity."

Black holes typically gobble up matter, which accelerates and heats up, emitting electromagnetic energy and creating some of the most luminous beacons in the sky called quasars. When two black holes orbit as a binary, they absorb matter cyclically, leading theorists to predict that the binary's quasar would respond by periodically brightening and dimming.

In this case, the scientists conducted a systematic search for variable quasars using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) Medium Deep Survey. In this data, they found quasar PSO J334.2028+01.4075, which has a very large black hole that emits a periodic optical signal every 542 days. This signal is somewhat unusual since the light curves of most quasars are arrhythmic. The scientists verified their finding with additional calculations.

In the end, the researchers believe that they found a binary supermassive black hole. This could tell them a bit more about how black holes merge.

"The discovery of a compact binary candidate supermassive black hole system like PSO J334.2028+01.4075, which appears to be at such close orbital separation, adds to our limited knowledge of the end stages of the merger between supermassive black holes," said Tingting Liu, the paper's first author.

The findings are published in The Astrophysical Journal.

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